Xerostomia, or dryness of the mouth, is a commonly experienced complaint which is characterised by diminished or arrested salivary secretion.
Saliva is secreted from numerous salivary glands, principally from the parotid, the submandibular and the sublingual salivary glands, as well as numerous minute accessory salivary glands situated just beneath the oral mucosa.
The principal functions of saliva are to keep the mucous membrane of the mouth moist, lubricate food during mastication, protect the teeth and aid the preliminary digestion of starch.
The immediate consequences of the xerostomia thus include difficulties in chewing, swallowing, speaking and interruptions of sleep patterns. More seriously, however, xerostomia has been known to result in ulcerations of the oral mucosa, dental problems including dental caries, increased frequencies of Candida, infections by Staphylococcus bacteria and, as a result of the latter, halitosis.
The causes of xerostomia are various and the condition may be subclassified along etiological lines.
Primary xerostomia arises as a consequence of pathological processes (e.g. atrophy or disease) resulting in hypofunction of the salivary glands. Primary xerostomia is also prevalent in patients having rheumatic disease (e.g. Sjogren's syndrome) as well as those undergoing radiotherapy for head and neck cancer.
The incidence of primary xerostomia is known to increase with age. For example in Sweden 15% of persons over 50 years of age complain about dryness of the mouth. This increases to 25% in persons above 70, and 33% of those above 80 years of age. As much as 40% of the hospitalised geriatric population of Sweden experience xerostomia.
Secondary xerostomia is a particularly common side effect experienced by patients taking certain pharmacological agents. Approximately half of all pharmacological agents are thought to cause xerostomia to some degree, although the problem is particularly prevalent in patients taking antidepressants and neuroleptics.
Currently available treatments for xerostomia are uncommon and include synthetic mucins (e.g. carmellose calcium, hypromellose and methylcellulose) and agents which act by reducing the viscosity of saliva in the patient's mouth (e.g. calcium sulphocyanide hexamethylenediamine; Mucidan.RTM.).
More recently pilocarpine hydrochloride has been made available for the systemic treatment of xerostomia resulting from radiotherapy. However, pilocarpine is known to produce adverse side effects involving the heart, blood pressure and digestion. Even in small daily doses, pilocarpine is known to produce profuse perspiration. U.S. Pat. No. 5,387,614 discloses the systemic treatment of xerostomia with sigma receptor ligands, namely N,N-disubstituted alkyl phenylamines, to patients.
Cholinesterase inhibitors (hereinafter designated CEIs) are known to be useful in the treatment of inter alia myasthenia gravis, glaucoma and intestinal paresis.
Pyridostigmine, a choline esterase inhibitor, have been used in patients with xerostomia, see e.g. Ferguson, M. M., Oral Surg. Oral Med. Oral Pathol., 1993:75, 191. Sustained release tablets were given orally to patients causing increase in salivary flow and increase in tear production, with variable reponse between individual patients.
Thus, there remains a need for a treatment for xerostomia which is effective and does not produce significant side effects.
Surprisingly, we have now found that CEIs are highly effective in the treatment of xerostomia, without producing any significant side-effects when administered directly to the oral mucosa, particularly at the sites of accessory salivary glands in order to stimulate salivary secretion and eliminate xerostomia.